Increasingly stringent emissions requirements are constantly pressuring researchers to perfect existing ways, and devise new ways, to reduce undesirable emissions. Among these undesirable emissions are particulate matter and NOx. Although there has been much progress in developing methods of operating internal combustion engines in ways that reduce undesirable emissions, it may be impossible to develop a fossil fuel combustion strategy that completely avoids the production of undesirable emissions. Therefore, much effort has been directed to aftertreatment strategies that remove or change undesirable emissions into more acceptable chemical compounds before the exhaust is vented to atmosphere.
One strategy that has been commercially utilized for reducing NOx emissions has been to react NOx in the exhaust with a reductant, such as urea, in the presence of an appropriate catalyst to produce nitrogen and water. While these systems can be somewhat effective, they are problematic in that they require an external urea tank that must be periodically refilled. Another potential reductant could be ammonia, but any supply strategy that requires the refilling of reductant tanks to maintain a supply also requires an infrastructure to support motorized vehicles that require a reductant resupply.
Current strategies for reducing particulate matter emissions often involve the use of particle traps that trap the particles before they can be vented to atmosphere. While this strategy can be quite effective, such traps often require periodic regeneration by burning to oxidize the particles. These regeneration strategies often require some open or closed loop control system for periodically regenerating the particle trap. These control systems can fail, and even if they do not fail, these particle traps cyclically apply increased back pressure on the engine which decreases efficiency to some measurable extent. In some instances, particularly at prolonged low load conditions, there may not be enough heat generated by the engine to regenerate the particle trap without some auxiliary heat source or by temporarily increasing engine output for the sole purpose of particle trap regeneration.
The present disclosure is directed to one or more of the problems set forth above.